1. Field of the Invention
Various embodiments of the subject invention relate to gaskets and, more particularly, to gaskets for inhibiting and preventing leakage of Electromagnetic Interference (EMI) and radio frequency radiation (RFI) between two surfaces or components.
2. Description of the Invention Background
Ever since Benjamin Franklin flew his famous kite in a lightening storm and discovered electricity, countless numbers of electrically powered devices and components have been developed to make man's life easier. Such components range from, for example, motors, switches, relays, timers, computers, etc. Indeed, the list of electrical components seems endless and continues to grow.
With the development and use of such a myriad of electronic components came additional problems that had to be solved to effectively use such components to achieve desired results. An example of one problem is the occurrence of electromagnetic interference (EMI) which is an undesirable electric disturbance that is induced or radiated from electric or electronic devices. Such EMI problems commonly manifest themselves when several electrical components are located in close proximity to one another wherein the EMI radiating from one component hampers or debilitates the effective operation of another component mounted nearby.
To combat problems encountered by EMI, electrical components are often placed or mounted in shielded housings that serve to prevent or inhibit the leakage of EMI therefrom. Such housings are commonly made from a collection of conductive panels that are connected together to form an enclosure. To prevent or inhibit the leakage of EMI between the panels at their points of connection and to prevent the leakage of EMI, for example, between a housing and the housing door, a variety of gaskets have been developed.
One type of gasket that has been developed is illustrated in FIG. 1. As shown in this Figure, gasket 1 includes a resilient or flexible core 2 that is covered by an electrically conductive cover 3. The core 2 generally comprises conventional open cell or closed cell foams, rubbers, plastics or metals and the electrically conductive cover 3 may comprise plated fabric (woven or knitted), plated plastic, plated rubber, electrically conductive foil, electrically conductive woven wire or electrically conductive wire mesh. These gaskets 1 are commonly affixed to the electrically conductive surface 10, which may comprise a cabinet panel, doorframe, etc. (depending upon the particular application) by adhesive 4 or other fastening medium. Such adhesives 4 or fastener means commonly comprise pressure sensitive adhesive, electrically conductive heat activated adhesive or a variety of other types of mechanical fasteners such as clips, screws or rivets.
Such attachment approaches, however, can undesirably form a barrier between the electrically conductive cover material 3 and the electrically conductive surface 10. If a conductive path is not established between the cover material 3 and the conductive surface 10 to which the gasket 1 is attached, the gasket's effectiveness is compromised and, in extreme cases, may be destroyed. Furthermore, when employing the prior gaskets of this type, the gaskets rely on the compression of the gasket 1 to force portions 6, 8 of the gasket 1 to flow around the adhesive 4 or mechanical fastener to make sufficient electrical contact with the electrically conductive surface 10. See FIG. 2. Such standard approach of relying on the flowing of portions 6, 8 of the gasket core 2 can result in the failure to establish an electrically conductive path between the electrically conductive surface 10 and the electrically conductive cover 2 when an insufficient amount of compression force F is applied to the gasket 1. One approach to addressing such problem has included the use of conductive pressure sensitive adhesive, which essentially contains conductive particles in the adhesive. Furthermore, if an electrically conductive adhesive is employed to affix the gasket 1 to the electrically conductive surface 10 and to establish an electrically conductive path therebetween, migration of the electrically conductive particles in the adhesive material can occur and compromise the integrity of the electrically conductive path. For example, when placed under continuous pressure, the conductive particles in the adhesive tend to migrate to certain areas and create portions of adhesive that have more conductive particles than other portions of the adhesive. If the portion containing the abundance of conductive particles fails to make effective contact with the gasket cover, no conductive path from the element to which the gasket is attached and the gasket cover may be established.
U.S. Pat. No. 5,578,790 purports to disclose a gasket to address such problems, by employing a pre-shaped inner core with an “extension” protruding from the attachment side. However, this approach may also have undesirable limitations. For example, this gasket requires a specific shape and a particular pressure sensitive attachment method. Moreover, the tolerances that are commonly attainable utilizing known gasket manufacturing processes, make this gasket difficult to manufacture in relatively small sizes. In addition, if the compression forces applied to the gasket when in use are not uniformly applied across the gasket, “rocking” may occur which results in one or more portions of the gasket being moved out of contact with the surface to which it is to be attached. In addition, the shape of the gasket limits the types and shapes of mechanical fasteners that may be employed to attach the gasket to an object. The gaskets disclosed in U.S. Pat. No. 5,105,056 to Hoge and U.S. Pat. No. 6,653,556 to Kim have many similar limitations.